In order to provide a solar cell watch in which the dial of the solar cell watch is visible as a metal plate and the deep purple of the solar cell is invisible, there is proposed a dial of solar cell shown in FIG. 49. The dial comprises a transmissive substrate 1 made of transparent plastic and a metal film 2 formed on the underside of the substrate and having a plurality of small apertures 2a disposed at regular intervals. The diameter of the aperture 2a is smaller than 30 μm. If the diameter is smaller than 30 μm, the aperture is invisible, and hence the solar cell disposed under the dial is also invisible.
Generally, the solar cell is equally divided into four divisions A1, A2, A3 and A4 as shown in FIG. 50. The quantity of light passing through the dial is equally irradiated to the four divisions. By disposing the small apertures 2a at regular intervals, four divisions are equally irradiated by the transmission light. The total area of small aperture is set to a range between 25 and 50% of the total area of the dial. If the total area of the small aperture 2a is set to 25%, transmittance of 25% is secured, which ensures sufficient generated energy. If the total area of the small aperture exceeds 50%, the deep purple of the solar cell is visible.
In a manufacturing process for such a dial for the solar cell, a number of steps and a high manufacturing cost are necessary. Furthermore, since the aperture is very small, it is difficult to make the dial at high accuracy. Consequently, the manufacturing process is low in yield and improper in mass production. Further, etching agent and stripping agent used in the process are ill for the human body.
An object of the present invention is to provide a dial for a watch and a manufacturing method for the dial may be manufactured by a simple process at a low cost at high accuracy without injury to the human body.